In many daily situations it is desirable to be able to determine the current position of a person or an object. For instance, a person who is new to a town and who does not know how to find his way to a specific location may be assisted by the provision of his current geographic position and the position of the specific location in question. Another situation when a person's current position is of interest is when traveling by car in an unfamiliar place. The current position of the person and the geographic position of the destination will assist the person in finding his way towards the destination.
When using an electronic device with a graphical interface, acquired position data are often graphically superimposed on a map before being provided to a user, thereby making it possible for the user to determine the best suitable way to travel. In some cases the position data and the map information may be further utilized in order to provide the user with direction guidance, i.e. Instead of merely showing the user's current position, the system may provide suggestions e.g. When to turn left or right.
Another, more important situation in which the position of a person is of interest is in case of emergency. If a person makes an emergency call (e.g. 911 in the United States or 112 in Europe) from a stationary telephone connected to the PST (Public Switched Telephone Network), the position of the caller is easy to determine due to the provision of ANTI (Automatic Number Identification) and possibly AIL (Automatic Location Identification) to the emergency call center. When an emergency call originates from a residential stationary telephone, the emergency call center receives the caller's telephone number and address hence making it possible to direct the help needed to the correct location.
However, in case a person makes an emergency call from a mobile telephone the position of the caller is much harder to determine with sufficient accuracy. In order to obtain a rough estimation of the caller's position it is possible to find out which base station that is currently serving the mobile terminal, and consequently also the cell in which the mobile telephone is operating. However, the size of the cell may vary from a few hundred meters to several kilometers depending on terrain, capacity demands, etc.
So as to provide more accurate positioning of a mobile terminal different techniques have been employed in the art. Generally, network-based methods or handset-based methods or hybrid methods combining the two are used for determining the position of a mobile terminal.
Among the network-based methods, TOGA (Time Difference of Arrival) which measures the difference between signal arrival times between different base stations, TAO (Time of Arrival) which measures absolute arrival times rather than time differences, ABA (Angle of Arrival) which use antenna arrays to determine a signal's incident angle, and Multi-path interference which records “fingerprints” from different locations, are widely used for more accurate determination of the position of a mobile terminal.
Correspondingly, among handset-based methods, E-OTD (Enhanced Observed Time Difference) which measures the relative time of arrival of signals from multiple mutually asynchronous base stations and A-FELT (Advanced Forward-Link Trilateration) which measures the phase delay between pairs of pilot signals in a synchronous mobile telephone network such as UMTS (Universal Mobile Telecommunications System), are widely used for making it possible for the mobile terminal to know its position. Yet another approach is to use GPS (Global Positioning System) which is very accurate, but at the same time is very slow, i.e. the time needed for determining the current position of the GPS receiver may be several minutes which is far too long in case of emergency.
Although systems for providing positioning services exist, the network-based techniques mentioned above are not implemented in all mobile telecommunications networks. Similarly, far from all mobile terminals used today are enabled to determine their location by means of the handset-based technologies. In case of emergency the consequences of not being able to report the correct position of an accident to the emergency call center due to the lack of positioning capabilities may be a matter of life and death. Consequently, there is a great need for techniques that may provide emergency call centers with accurate information regarding the position of the calling mobile terminal. For example, the FCC (Federal Communications Commission) requires network-based location systems to provide the position of the calling mobile terminal within a tolerance of 50 m for 65% of the calls and 150 m for 95% of the calls.
Moreover, besides in case of emergency, positioning capabilities may be used in a broader scale, wherein the position of the mobile terminal may be used for presenting any kind of location information to the user, i.e. in addition to the current position, ads or offers specific to the region the user is traveling in may be presented by the provision of location based services. Other location bases services include traffic advisory, navigation help, and roadside assistance. Mobile terminals not enabled for location based services will hence not be able to provide possibly valuable local information to the user thereof.